The Patent Document 1 describes an asymmetric gas separation membrane obtained by a heat treatment of infusibilization an asymmetric membrane composed of substituted polyimide having at a temperature in a range from 270 to 450° C. and lower than the glass transition temperature of the polyimide. This gas separation membrane had a practical capability to separate and collect organic vapor because the membrane has been improved in solvent resistance and had a high permeance for methanol vapor.
However, there have been problems of embrittlement and deterioration in mechanical strength when polyimide has been infusibilized by a heat treatment at a high temperature as described above.
On the other hand, the Patent Document 2 and the Patent Document 3 describe an asymmetric hollow fiber gas separation membrane, which is formed of polyimide consisting of a particular aromatic tetracarboxylic acid component and aromatic diamine, and which has an excellent ratio of the permeance for oxygen gas to the permeance for nitrogen gas. The Patent Document 4 also describes a method for producing a polyimide asymmetric membrane consisting of multicomponent polyimides.
However, the separation membranes described in these references are insufficient in solvent resistance, which need further improvement for separating and collecting organic vapor.    Patent Document 1; JP A 2004-267,810    Patent Document 2; JP A H03-267,130    Patent Document 3; JP A H06-254,367    Patent Document 4; JP A 2006-224,097